1. Field of the Invention
The present invention is directed to enzymatic methods of preparing aldehydes from fatty acids.
2. Description of Related Art
Microorganism-produced enzymes are widely used as a class of biocatalytic reagents in synthetic organic chemistry in a variety of reactions including, e.g., oxidations, reductions, hydrolyses, and carbon-carbon bond ligations. For example, enzyme reactions catalyzed by esterases may be used either hydrolytically or to synthesize esters, depending on whether the reaction medium is aqueous or organic in composition.
Biocatalysts are valued for their intrinsic abilities to bind organic substrates and to catalyze highly specific and selective reactions under the mildest of reaction conditions. These selectivities and specificities are realized because of highly rigid interactions occurring between the enzyme active site and the substrate molecule. Biocatalytic reactions are particularly useful when they are used to overcome difficulties encountered in catalysis achieved by the use of traditional chemical approaches.
The reduction of carboxylic acids by microorganisms is a relatively new biocatalytic reaction that has not yet been widely examined or exploited. Jezo and Zemek reported the reduction of aromatic acids to their corresponding benzaldehyde derivatives by Actinomycetes in Chem. Papers 40(2):279-281 (1986). Kato et al. reported the reduction of benzoate to benzyl alcohol by Nocardia asteroides JCM 3016 (Agric. Biol. Chem. 52(7):1885-1886 (1988)), and Tsuda et al. described the reduction of 2-aryloxyacetic acids (Agric. Biol. Chem. 48(5):1373-1374 (1984)) and arylpropionates (Chem. Pharm. Bull. 33(11):4657-4661 (1985)) by species of Glomerella and Gloeosporium. Microbial reductions of aromatic carboxylic acids, typically to their corresponding alcohols, have also been observed with whole cell biotransformations by Clostridium thermoaceticum (White et al., Eur. J. Biochem. 184:89-96 (1989)) and by Neurospora (Bachman et al., Arch. Biochem. Biophys. 91:326 (1960)). More recently, carboxylic acid reduction reactions have reportedly been catalyzed by whole cell preparations of Aspergillus niger, Corynespora melonis and Coriolus (Arfmann et al., Z. Naturforsch 48c:52-57 (1993); cf., Raman et al., J. Bacterial 84:1340-1341 (1962)), and by Nocardia (Chen and Rosazza, Appl. Environ. Microbiol. 60(4):1292-1296 (1994)).
Carboxylic acid reductases are complex, multicomponent enzyme systems requiring the initial activation of carboxylic acids via formation of acyl-AMP and often coenzyme A intermediates (see, e.g., Hempel et al., Protein Sci. 2:1890-1900 (1993). The enzymatic reaction offers significant advantages over existing methods used in chemical reductions of carboxylic acids or their derivatives. The carboxylic acid reduction reaction appears to bear the usual desirable features of functional group specificity, and it also functions well under mild reaction conditions and produces a high yield of product. The reduction of the activated carboxylic acid intermediate occurs step-wise to give aldehyde, and then alcohol, products (Gross et al., Eur. J Biochem. 8:413-419; 420-425 (1969); Gross, Eur. J. Biochem. 31:585-592 (1972)).
Fatty alcohols and aldehydes can be commercially produced using one of several methods. However, one of the most widely used commercial methods, catalytic hydrogenation of fatty acids and methyl esters from fats and oils, produces fatty alcohols using high pressures (typically, 25,000-30,000 kP) and high temperatures (typically 250-300° C.). See, e.g., “Fatty Acids and Derivatives from Coconut Oil,” in Bailey's Industrial Oil and Fat Products, 5th ed., Volume 5, Y. H. Hui, ed., John Wiley & Sons, Inc. (1996). The high pressures and temperatures employed in these methods are harsh in comparison to the milder conditions common with enzymatic reactions and can lead to unwanted side reactions, such as isomerization of one or more double bonds present in unsaturated fatty acid starting materials.
There continues to exist a need for improved methods of producing fatty alcohols and aldehydes with improved reaction specificity that lead to higher yields and fewer side reactions.